Lithium ion battery positive electrode material, preparation method thereof and lithium ion battery

Abstract

The invention provides a lithium ion battery positive electrode material, a preparation method thereof and a lithium ion battery. The lithium ion battery positive electrode material comprises a base material and a plurality of coatings distributed on the surface of the base material in a discrete mode, the coatings comprise fluorine-containing silane, the mass ratio of the base material to all the coatings is 1: (0.001-0.25), the shortest distance L between any two adjacent coatings is larger than or equal to 5 nm and smaller than or equal to 1000 nm. The lithium ion battery positive electrode material provided by the invention has the fluorine-containing silane coating in discrete distribution, and a super-hydrophobic surface layer is constructed on the surface of the base material, so that the lithium ion transmission efficiency of the lithium ion battery positive electrode material can be improved while the base material and moisture are effectively blocked, and the service life of the lithium ion battery positive electrode material is prolonged. Therefore, the air stability, the cycle stability and the charge-discharge performance of the lithium ion battery positive electrode material are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a lithium ion battery positive electrode material, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] With the rapid development of new energy technology, lithium ion batteries, as efficient energy storage devices, have been widely used in electric vehicles, portable electronic devices and energy storage systems. As a core component of lithium ion batteries, the performance of the positive electrode material directly affects the energy density, cycle life and safety of the battery.

[0003] However, during the preparation and storage of the positive electrode material, moisture in the air has many adverse effects on the performance of the positive electrode material, such as decreased preparation efficiency, decreased safety performance, and decreased conductivity. SUMMARY

[0004] In view of this, in order to solve at least one of the above technical problems, the present application provides a lithium ion battery positive electrode material.

[0005] In addition, the present application also provides a preparation method of the lithium ion battery positive electrode material and a lithium ion battery.

[0006] In a first aspect, the present application provides a lithium ion battery positive electrode material, which comprises a base material and a plurality of discrete coating materials distributed on the surface of the base material, the coating material comprises fluorine-containing silane, and the mass ratio of the base material to all the coating materials is 1: (0.001-0.25), the shortest distance between any two adjacent coating materials is L, and L satisfies 5nm≤L≤1000nm.

[0007] Based on the first aspect, in some possible embodiments, the mass ratio of the base material to all the coating materials is 1: (0.02-0.12), and L satisfies 10nm≤L≤500nm.

[0008] Based on the first aspect, in some possible embodiments, the coating material is in the form of point coating and / or island coating on the surface of the base material.

[0009] Based on the first aspect, in some possible embodiments, the maximum thickness of each coating material is d, and d satisfies 2nm≤d≤100nm.

[0010] Based on the first aspect, in some possible embodiments, the surface roughness of the lithium ion battery positive electrode material is Ra, and Ra satisfies 33nm≤Ra≤300nm.

[0011] In some possible embodiments based on the first aspect, each of the cladding materials has a size of micrometer or nanometer.

[0012] In some possible embodiments based on the first aspect, the fluorine-containing silane includes at least one of 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane, 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane, heptadecafluorodecyltrimethoxysilane, dodecafluoroheptylpropyltrimethoxysilane, and dimethyl-y-perfluorooctanoyloxypropylchlorosilane.

[0013] In a second aspect, the present application provides a preparation method of a lithium ion battery cathode material, including: mixing a precursor of a lithium ion battery cathode material and a lithium source and performing first sintering to obtain a base material; mixing the base material and a cladding material to obtain a mixture, wherein a mass ratio of the base material to the cladding material is 1: (0.001-0.25), and the cladding material includes a fluorine-containing silane; and performing second sintering on the mixture to make the cladding material form a plurality of discrete cladding materials distributed on a surface of the base material, so as to obtain the lithium ion battery cathode material, wherein a shortest distance between any two adjacent cladding materials is L, and L satisfies: 5 nm≤L≤1000 nm.

[0014] In some possible embodiments based on the second aspect, the second sintering includes first sintering and second sintering performed in sequence, wherein a pressure of the first sintering is 1 Pa-15 Pa, and a pressure of the second sintering is -30 Pa--5 Pa.

[0015] In some possible embodiments based on the second aspect, a temperature of the first sintering is 50℃-300℃, and a time of the first sintering is 0.5 h-10 h; a temperature of the second sintering is 200℃-500℃, and a time of the second sintering is 2 h-10 h.

[0016] In a third aspect, the present application also provides a lithium ion battery, including a positive electrode sheet, and the positive electrode sheet includes a positive electrode material, and the positive electrode material is the lithium ion battery cathode material or the lithium ion battery cathode material prepared by the preparation method.

[0017] Compared with the prior art, the lithium ion battery positive electrode material provided by the embodiment of the application can effectively form a super-hydrophobic surface layer on the surface of the base material by discrete coating of the fluorine-containing silane on the base material, and the mass ratio of the base material to the entire coating is 1:(0.001-0.25), and the shortest distance L between any two adjacent coatings satisfies 5nm≤L≤1000nm, so that the base material is protected from moisture erosion, and the air stability and cycle stability of the lithium ion battery positive electrode material are improved. At the same time, the surface of the base material has a proper uncoated area, which provides a channel for the diffusion of lithium ions, reduces the influence of the inert coating fluorine-containing silane on the electrical properties of the lithium ion battery positive electrode material, and is beneficial to improving the charge-discharge performance of the lithium ion battery positive electrode material. The discrete coating structure adopted by the application not only improves the hydrophobic performance of the lithium ion battery positive electrode material, but also improves the electrical performance of the lithium ion battery positive electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The process flow chart of the preparation method of the lithium ion battery positive electrode material provided by an embodiment of the application.

[0019] Figure 2 The field emission microscope image of the lithium ion battery positive electrode material in Example 1 of the application.

[0020] Figure 3 The X-ray diffraction pattern of the lithium ion battery positive electrode material in Example 1 of the application.

[0021] Figure 4 The field emission microscope image of the lithium ion battery positive electrode material in Example 2 of the application.

[0022] Figure 5 The field emission microscope image of the lithium ion battery positive electrode material in Comparative Example 1 of the application.

[0023] Figure 6 The cycle performance test chart of the lithium ion battery prepared by the lithium ion battery positive electrode material in Examples 1-2 and Comparative Example 1 of the application.

[0024] Figure 7 The charge-discharge curve of the lithium ion battery prepared by the lithium ion battery positive electrode material in Example 1 and Comparative Example 2 of the application. DETAILED DESCRIPTION

[0025] Embodiments of the present application are described in detail below. The embodiments described below with reference to the drawings are exemplary only, and are intended to explain the present application, and are not to be understood as limiting the present application; it should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs; the embodiments of the present application and the features in the embodiments can be combined with each other without conflict, if necessary; in the following description, a large number of specific details are set forth in order to fully understand the present application, and the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments.

[0026] The present application researches and finds that the moisture in the air has a serious influence on the performance of the lithium ion battery cathode material. For example, the moisture can cause the increase of the residual lithium carbonate and lithium hydroxide and other alkaline substances on the surface of the high-nickel ternary cathode material, so that the viscosity of the cathode material increases during the slurry preparation, and after the battery is prepared, problems such as the increase of lithium salt consumption, the initiation of side reactions, the increase of battery internal resistance, high self-discharge, rapid attenuation, and even safety problems such as swelling, shell bulging, and liquid leakage can occur; the lithium iron phosphate cathode material is affected by the moisture, and problems such as local change of crystal structure, increase of internal resistance, and surface corrosion can occur; the lithium iron manganese phosphate cathode material is easy to absorb water gel, which causes large change of slurry viscosity, affects the coating efficiency and energy density of the battery cell, and the moisture can also cause a series of adverse reactions during the calcination process, affecting the conductivity of the cathode material.

[0027] Therefore, the embodiments of the present application provide a lithium ion battery cathode material, which comprises: a base material and a plurality of discrete coating materials distributed on the surface of the base material, the coating material comprises fluorine-containing silane, the mass ratio of the base material to all the coating materials is 1: (0.001-0.25), and the shortest distance between any two adjacent coating materials is L, which satisfies: 5 nm≤L≤1000 nm.

[0028] The coating material comprises fluorine-containing silane, which is a kind of compound with low surface energy and good chemical stability. The fluorine-containing silane is discretely coated on part of the surface of the base material, which can long-acting block the direct contact of the base material with air, moisture and electrolyte, and improve the structural stability and cycle stability of the lithium ion battery cathode material. Specifically, on the one hand, the fluorine-containing silane can react with the hydroxyl group on the surface of the base material, directly reducing the content of the alkaline impurities already generated on the surface of the base material. On the other hand, the fluorine-carbon chain (—(CF2) nThe fluorine-containing silane effectively reduces the surface energy of the fluorine-containing silane and imparts excellent hydrophobicity to the fluorine-containing silane, so that a stable hydrophobic interface is formed on the surface of the base material, water adsorption and reaction are prevented, the generation of alkaline impurities on the surface of the lithium ion battery cathode material during storage is reduced, the side reaction in the battery and the dissolution of transition metals are reduced, and the cycle stability and safety performance of the lithium ion battery cathode material are improved. At the same time, the fluorine-containing silane can also prevent the base material from directly contacting the electrolyte, inhibit the corrosion of the electrolyte decomposition product (such as HF) on the base material, maintain the integrity of the structure of the lithium ion battery cathode material, and further improve the cycle performance of the lithium ion battery cathode material. In addition, the good chemical stability of the fluorine-containing silane enables it to maintain a high integrity of the coating during battery use, thereby reducing the generation of side reactions between the base material and air, water and electrolyte during long-term cycling, and further improving the structural stability and cycle stability of the lithium ion battery cathode material.

[0029] Specifically, the fluorine-containing silane can include at least one of 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane, 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane, heptadecafluorodecyltrimethoxysilane, dodecafluoroheptylpropyltrimethoxysilane, and dimethyl-y-perfluorooctanoyloxypropylchlorosilane.

[0030] In addition, since the coating is distributed in a discrete manner on the surface of the base material, a large number of grooves are formed on the surface of the lithium ion battery cathode material, increasing the roughness of the surface of the cathode material. The high roughness, combined with the fluorine-containing silane in the coating, synergistically improves the hydrophobicity of the surface of the cathode material, so that the surface of the cathode material achieves super-hydrophobicity. At the same time, the discrete coating structure also forms many uncovered areas on the surface of the cathode material, providing a channel for the diffusion of lithium ions, which is beneficial to improving the charge and discharge performance of the cathode material. Compared with a continuous and complete coating layer, the lithium ion battery cathode material of the present application has a discrete coating structure, which not only further improves the hydrophobicity of the cathode material, but also reduces the influence of the inert coating layer on the electrical performance of the cathode material, and balances the hydrophobicity and charge and discharge performance of the cathode material.

[0031] Further, the plurality of coatings on the surface of the base material can be point-like coatings or island-like coatings. The point-like coating refers to the coating being attached to the surface of the base material in the form of discontinuous and isolated points, and having a small size and a shape close to a circle. The island-like coating refers to the coating being attached to the surface of the base material in the form of isolated island-like structures, and having a wide size range and an irregular shape.

[0032] In the lithium ion battery cathode material, the mass ratio of the base material to the coating is 1: (0.001-0.25), which is conducive to the formation of discrete coating and the adjustment of the distance between any two adjacent coatings, so as to more easily control the size of the shortest distance L between the two adjacent coatings to meet 5nm≤L≤1000nm. If the ratio is too large, i.e. the proportion of the coating is too small, it is easy to cause L to be too large, the coating to be too discrete, and it is difficult to effectively protect the base material; if the ratio is too small, i.e. the proportion of the coating is too large, it is easy to cause L to be too small, the coating to be too continuous, and hinder the transmission of lithium ions. The mass ratio of the base material to the coating can exemplarily be 1:0.001, 1:0.005, 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.08, 1:0.1, 1:0.12, 1:0.15, 1:0.18, 1:0.2, 1:0.22, 1:0.25, or any value within the range composed of any two of the above values. The mass ratio of the base material to the coating can further be 1: (0.02-0.12).

[0033] Specifically, the shortest distance L between any two adjacent coatings meets: 5nm≤L≤1000nm, if the distance between the two adjacent coatings is too large (L is greater than 1000nm), the hydrophobic effect of the cathode material surface will be greatly weakened, and it is difficult to effectively form a hydrophobic interface to isolate water; if the distance between the two adjacent coatings is too small (L is less than 5nm), since the fluorine-containing silane also has certain oil-repellent properties, it will cause the dispersion of the cathode material in the slurry during the production of the electrode sheet to be weakened, affect the coating uniformity of the electrode sheet, make the battery performance unable to normally play, and the small distance between the two adjacent coatings will also cause the lithium ion transmission channel to be too small, reducing the charge and discharge performance of the cathode material. L can exemplarily be 5nm, 10nm, 50nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm, or any value within the range composed of any two of the above values. L can further be 10nm-500nm, which is conducive to better balancing the hydrophobic property and the ion transmission property.

[0034] In some embodiments, the maximum thickness of the coating is d, which can meet: 2nm≤d≤100nm, which is conducive to protecting the base material from the external environment, and also conducive to balancing the good intrinsic performance of the cathode material, such as low interface impedance and high lithium ion transmission efficiency. d can exemplarily be 2nm, 5nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, or any value within the range composed of any two of the above values. d can further be 5nm-40nm.

[0035] In some embodiments, the surface roughness of the lithium ion battery cathode material is Ra, and Ra can satisfy: 33nm≤Ra≤300nm. By controlling the aforementioned distance L, a large number of grooves can be formed on the surface of the base material, so that the lithium ion battery cathode material has a higher roughness, and the hydrophobicity of the surface of the cathode material can be further enhanced, and even reach a super-hydrophobic state.

[0036] In some embodiments, the coating can be a micro-nano structure, which refers to a structure with a size in the micron or nanometer level. The micro-nano structure can improve the contact angle of water droplets on the lithium ion battery cathode material, thereby improving the hydrophobicity of the surface. That is, the size of each coating is micron or nanometer level.

[0037] In some embodiments, the base material can include at least one of nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, lithium iron phosphate, and manganese iron lithium phosphate.

[0038] Please refer to Figure 1 Based on the same inventive concept, the embodiments of the present application also provide a preparation method of a lithium ion battery cathode material, which specifically includes the following steps: Step S1, mixing a precursor of a lithium ion battery cathode material and a lithium source and performing first sintering to obtain a base material.

[0039] In some embodiments, the lithium source can include at least one of lithium hydroxide, lithium carbonate, etc.

[0040] In some embodiments, the temperature of the first sintering can be 600°C~950°C, and the time of the first sintering can be 18h~35h. The temperature of the first sintering can exemplarily be 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, or any value within the range consisting of any two of the above values; the time of the first sintering can exemplarily be 18h, 22h, 26h, 30h, 35h, or any value within the range consisting of any two of the above values. By adjusting the temperature and time of the first sintering to satisfy the above range, the present application is beneficial to fully lithiate the lithium ion battery cathode material precursor, and form a base material with low defects and complete and stable structure.

[0041] Step S2, mixing the base material and a coating material to obtain a mixture, wherein the mass ratio of the base material to the coating material is 1:(0.001~0.25), and the coating material includes fluorine-containing silane.

[0042] In some embodiments, the hydroxyl ions (OH -The molar ratio of the fluorine-containing silane can be 1: (1.05-1.35), which is conducive to the reaction of the fluorine-containing silane with the OH groups on the surface of the matrix material - and reduces the residual alkali content without introducing excessive fluorine-containing silane. The OH content in the matrix material can be measured by acid-base titration. - The molar ratio of the fluorine-containing silane can be 1:1.05, 1:1.10, 1:1.15, 1:1.20, 1:1.25, 1:1.30, 1:1.35, or any value within the range defined by any two of the above values. The OH content in the matrix material can be measured by acid-base titration. - The OH content in the matrix material can be measured by acid-base titration.

[0043] In step S3, the mixture is subjected to secondary sintering to form a plurality of discrete coatings on the surface of the matrix material, thereby obtaining the lithium ion battery cathode material. The shortest distance between any two adjacent coatings is L, and L satisfies 5 nm≤L≤1000 nm.

[0044] Specifically, under an oxygen or air atmosphere, the mixture is subjected to secondary sintering by solid-phase sintering to form a plurality of discrete coatings on the surface of the matrix material. The fluorine-containing silane volatilizes into a free state upon heating, the alkoxy group of the fluorine-containing silane covalently bonds with the hydroxyl group on the surface of the matrix material, and the fluorine-containing silane spontaneously performs molecular self-assembly. For example, the head group (silane) forms a firm covalent bond with the hydroxyl group (-OH) on the surface of the matrix material through hydrolysis, and the tail group (fluorine-containing chain) with low surface energy spontaneously aligns towards the air side in order to minimize its interfacial energy, thereby modifying the hydrophobic group to the surface of the matrix material and constructing a surface hydrophobic interface. The mass ratio of the matrix material to the coating material in the mixture is 1: (0.001-0.25), which is conducive to the formation of discrete coatings (such as point-like coatings or island-like coatings) on the surface of the matrix material instead of continuous coatings, and is conducive to regulating the distance between any two adjacent coatings, so that L satisfies 5 nm≤L≤1000 nm.

[0045] Traditional methods such as solution method, atomic deposition (ALD), and magnetron sputtering can be used to deposit the fluorine-containing silane coating. However, the fluorine-containing silane is an inert material, and the continuous and dense coating formed on the surface of the matrix material will hinder the transmission of lithium ions, causing the electrical performance of the cathode material to deteriorate. Moreover, the above methods have the disadvantages of multiple preparation procedures, high equipment cost, and complex operation, which makes it difficult to achieve large-scale production. The present application utilizes the solid-phase method and the self-assembly characteristics of the fluorine-containing silane to simply and conveniently achieve point-like or island-like coating on the surface of the matrix material at a low cost, thereby balancing the surface hydrophobic performance and electrochemical performance of the lithium ion battery cathode material.

[0046] In some embodiments, the secondary sintering includes a first-stage sintering and a second-stage sintering performed in sequence, wherein the pressure of the first-stage sintering is 1 Pa to 15 Pa, and the pressure of the second-stage sintering is -30 Pa to -5 Pa. The pressure of the first-stage sintering can exemplarily be 1 Pa, 2 Pa, 3 Pa, 4 Pa, 5 Pa, 6 Pa, 7 Pa, 8 Pa, 9 Pa, 10 Pa, 11 Pa, 12 Pa, 13 Pa, 14 Pa, 15 Pa, or any value within a range consisting of any two of the above values. The pressure of the second-stage sintering can exemplarily be -30 Pa, -25 Pa, -20 Pa, -15 Pa, -10 Pa, -5 Pa, or any value within a range consisting of any two of the above values. In the first-stage sintering, the pressure of sintering (the pressure in the sintering device) is positive, the fluorine-containing silane is volatilized after being heated, is in a free state in the sintering device, the alkoxyl group of the fluorine-containing silane is covalently bonded to the hydroxyl group on the surface of the substrate material, and the fluorine-containing silane can spontaneously perform molecular self-assembly to modify the hydrophobic group to the surface of the substrate material. After sufficient reaction, the second-stage sintering is entered, in which the sintering pressure is negative, which is conducive to the removal of free fluorine-containing silane molecules that are not covalently bonded to the surface of the substrate material and are not involved in self-assembly from the reaction system, and further promotes the formation of discrete coating on the surface of the substrate material by the fluorine-containing silane that is covalently bonded to the surface of the substrate material and is involved in self-assembly.

[0047] In some embodiments, the temperature of the first-stage sintering can be 50°C to 300°C, which can exemplarily be 50°C, 80°C, 100°C, 150°C, 200°C, 250°C, 300°C, or any value within a range consisting of any two of the above values; and the time of the first-stage sintering can be 0.5 h to 10 h, which can exemplarily be 0.5 h, 1 h, 3 h, 5 h, 8 h, 10 h, or any value within a range consisting of any two of the above values. The present application adjusts the temperature and time of the first-stage sintering to meet the above range, which is conducive to heating the fluorine-containing silane to make it in a free state and promoting the bonding and self-assembly reaction of the fluorine-containing silane.

[0048] In some embodiments, the temperature of the second-stage sintering can be 200°C to 500°C, which can exemplarily be 200°C, 300°C, 400°C, 500°C, or any value within a range consisting of any two of the above values; and the time of the second-stage sintering can be 2 h to 10 h, which can exemplarily be 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, or any value within a range consisting of any two of the above values. The present application adjusts the temperature and time of the second-stage sintering to meet the above range, which is conducive to volatilizing the excess unreacted fluorine-containing silane and promoting the combination of the fluorine-containing silane and the substrate material, thereby improving the stability of the coating.

[0049] In some embodiments, the fluorine-containing silane can include at least one of 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane, 1H, 1H, 2H, 2H-perfluorodecanyltriethoxysilane, heptadecafluorodecyltrimethoxysilane, dodecafluoroheptylpropyltrimethoxysilane, and dimethyl-y-perfluorooctanoyloxypropylchlorosilane, etc. The above fluorine-containing silane has a tail carbon chain with a suitable length, which can better spontaneously perform molecular self-assembly.

[0050] Compared with the prior art, the preparation method of the lithium ion battery positive electrode material has the following beneficial effects: 1. The present application adopts a solid phase method and controls the ratio of the base material and the coating material, which is conducive to forming a discrete coating structure in the form of dots or islands on the surface of the base material, rather than a continuous coating, which is conducive to balancing the hydrophobicity and electrical performance of the lithium ion battery positive electrode material.

[0051] 2. The present application adopts two-stage secondary sintering and controls the gas pressure of the first-stage sintering and the second-stage sintering. The positive pressure of the first-stage sintering ionizes the fluorine-containing silane, which is conducive to promoting the covalent bonding of the fluorine-containing silane with the hydroxyl groups on the surface of the base material and promoting the self-assembly of the fluorine-containing silane. The negative pressure of the second-stage sintering is conducive to enhancing the bonding force between the coating and the base material and removing excess fluorine-containing silane, which is conducive to promoting the formation of a discrete coating structure.

[0052] 3. The preparation method of the present application also has the advantages of simple process, fewer process steps, low production cost, excellent electrochemical and hydrophobic performance of the prepared positive electrode material, and suitability for large-scale production, etc., and has good popularization and application value.

[0053] The present application also provides a lithium ion battery, which includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode material. The positive electrode material is the lithium ion battery positive electrode material described above or the lithium ion battery positive electrode material prepared by the preparation method described above. Compared with the prior art, the lithium ion battery provided by the present application has good air stability, cycle stability, and charge-discharge performance.

[0054] The scheme of the present application will be explained below in combination with embodiments. Those skilled in the art will understand that the following examples are only used to explain the present application and cannot be understood as a limitation of the present application. Unless otherwise indicated, the reagents, software and instruments involved in the following embodiments, which are not specifically indicated, are all conventional commercially available products or publicly known.

[0055] Example 1 Step S1, 2000.0 g of nickel-cobalt-manganese ternary positive electrode material precursor Ni 0.96 Co 0.03 Mn 0.01The 2000.0 g of the base material and 240 g of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane are mixed by a high-speed mixer at 500 rpm for 10 min to obtain a mixture.

[0056] Step S2, 2000.0 g of the base material and 240 g of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane are mixed by a high-speed mixer at 500 rpm for 10 min to obtain a mixture.

[0057] Step S3, the mixture is subjected to secondary sintering in an oxygen atmosphere (sintering furnace oxygen content above 99.95% and continuous oxygen supply), and the secondary sintering includes first-stage sintering and second-stage sintering performed in sequence. The first-stage sintering is performed at a sintering furnace pressure of 5 Pa, and the temperature is raised to 120°C at a rate of 5°C / min and held for 6 h. The second-stage sintering is performed at a sintering furnace pressure of -10 Pa, and the temperature is raised to 300°C at a rate of 5°C / min and held for 4 h, so that the coating material forms a plurality of discrete coatings distributed on the surface of the base material. Then, the temperature is lowered to room temperature at a rate of 3°C / min, and the lithium ion battery positive electrode material is obtained by sieving.

[0058] Example 2: The difference from Example 1 is that in Step S2, the mass of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane is 40 g. The rest of the lithium ion battery positive electrode material preparation method is basically the same as that of Example 1.

[0059] Example 3: The difference from Example 1 is that in Step S2, the mass of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane is 2 g. The rest of the lithium ion battery positive electrode material preparation method is basically the same as that of Example 1.

[0060] Example 4: The difference from Example 1 is that in Step S2, the mass of 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane is 500 g. The rest of the lithium ion battery positive electrode material preparation method is basically the same as that of Example 1.

[0061] Example 5: The difference from Example 1 is that in Step S3, the pressure of the first-stage sintering is 1 Pa, and the pressure of the second-stage sintering is -30 Pa. The rest of the lithium ion battery positive electrode material preparation method is basically the same as that of Example 1.

[0062] Example 6: The difference from Example 1 is that in step S3, the pressure of the first sintering is 15 Pa, and the pressure of the second sintering is -5 Pa. The rest of the preparation method of the lithium ion battery positive electrode material is basically the same as that of Example 1.

[0063] Comparative Example 1: Step S1, 2000.0 g of the precursor Ni 0.96 Co 0.03 Mn 0.01 (OH)2 and 1618.3 g of LiOH were mixed by a high-speed mixer at 700 rpm for 15 min, and then sintered at a speed of 10 ℃ / min to 760 ℃ under an oxygen atmosphere (the oxygen content of the sintering furnace is more than 99.95% and the oxygen is continuously supplied) for 14 h, and then cooled to room temperature at a speed of 3 ℃ / min, and then sieved to obtain the base material.

[0064] Step S2, the base material was sintered for the second time under an oxygen atmosphere (the oxygen content of the sintering furnace is more than 99.95% and the oxygen is continuously supplied), which includes first sintering and second sintering performed in sequence, wherein the pressure in the sintering furnace of the first sintering is 5 Pa, the temperature is raised to 120 ℃ at a speed of 5 ℃ / min and kept for 6 h, the pressure in the sintering furnace of the second sintering is -10 Pa, the temperature is raised to 300 ℃ at a speed of 5 ℃ / min and kept for 4 h, and then cooled to room temperature at a speed of 3 ℃ / min, and then sieved to obtain the lithium ion battery positive electrode material.

[0065] Comparative Example 2: The difference from Example 1 is that in step S2, the mass of 1H, 1H, 2H, 2H-perfluorodecanyl triethoxysilane is 800 g. The rest of the preparation method of the lithium ion battery positive electrode material is basically the same as that of Example 1.

[0066] Comparative Example 3: The difference from Example 1 is that in step S2, the mass of 1H, 1H, 2H, 2H-perfluorodecanyl triethoxysilane is 1 g. The rest of the preparation method of the lithium ion battery positive electrode material is basically the same as that of Example 1.

[0067] The lithium ion battery positive electrode materials obtained in Examples 1-6 and Comparative Examples 1-3 were tested as follows.

[0068] 1. Contact angle test: The material powder is placed in a cylindrical container, the surface is flattened, then deionized water is added to the surface with a dropper, and the contact angle is calculated by ImageJ software, 3 times for each sample, and the average value is taken as the test of the hydrophobic performance of the material.

[0069] 2. Lithium hydroxide dissolution (residual base content) test: using an acid-base titrator, the method specified in the standard drafted by the National Non-ferrous Metals Standardization Technical Committee, "Determination of magnetic foreign matter content and residual base content of lithium ion battery positive electrode material" is used for testing.

[0070] 3. X-ray diffraction test (XRD): an X-ray diffractometer with model D8 Advance is used for crystal structure analysis of the material sample.

[0071] 4. Field emission scanning electron microscope (FE-SEM) observation: a field emission scanning electron microscope with model SU8700 is used to observe the microstructure and structural characteristics of the material, and the shortest distance L between any two adjacent coatings on the surface of each particle and the thickness d of the coating are measured using Image J software, L is the shortest distance between any two adjacent coatings, and d is the distance from the highest point of the coating to the matrix material.

[0072] 5. Surface roughness test: a three-dimensional scanning electron microscope with model Regulus 8100 is used to test the surface roughness of the material.

[0073] 6. Electrical performance test: Preparation of button-type half-cell: lithium ion battery positive electrode material, conductive agent acetylene black and binder PVDF are weighed according to the mass ratio of 96.5:1.5:2, and the positive electrode sheet is coated and rolled in an argon atmosphere glove box, and button-type half-cell is assembled.

[0074] Under the condition of normal temperature battery laboratory, the button-type half-cell is charged at 0.1C constant current to voltage 4.3V, and charged at 4.3V constant voltage to current 0.02C, and then rested for 5min, and the charge capacity is recorded; then the button-type half-cell is discharged at 0.1C constant current to voltage 3.0V, and the discharge capacity is recorded, and the first cycle discharge gram capacity at 0.1C is calculated, and the first cycle coulombic efficiency = first cycle discharge gram capacity / charge capacity x 100%.

[0075] According to the above conditions, the charge and discharge cycle is carried out for 50 times, and the capacity retention rate after 50 cycles is calculated, and the capacity retention rate = 50th cycle discharge gram capacity / first discharge gram capacity x 100%.

[0076] 7. Storage performance test: The material is exposed to an air environment with humidity of 60%, and after 8 days of exposure, the surface residual base growth, moisture growth, and the discharge capacity of the battery and the capacity retention rate after 50 cycles are tested.

[0077] The surface residual alkali test refers to the aforementioned lithium hydroxide dissolution test method, and the surface residual alkali increase = the residual alkali content of the material after 8 days of exposure - the residual alkali content of the initial material.

[0078] The moisture test of the material: the moisture of the material is tested by Mettler Toledo V30S automatic Karl Fischer titrator, and the moisture increase = the moisture content of the material after 8 days of exposure - the moisture content of the initial material.

[0079] The test method of the discharge capacity of the material after 8 days of storage and the capacity retention rate after 50 cycles refers to the discharge capacity test and capacity retention rate test in the aforementioned electrical performance test.

[0080] The test results of examples 1-6 and comparative examples 1-3 are shown in tables 1, 2, 3 and Figures 2 to 7

[0081] Table 1 Note: " / " indicates that the sample does not have this parameter or test result.

[0082] Table 2 Table 3 The above results show that: As can be seen from tables 1 to 3, compared with comparative examples 1-3, the shortest distance L between any two adjacent coatings of the lithium ion battery positive electrode material in examples 1-6 satisfies 5nm≤L≤1000nm, so that the coating effectively forms a super-hydrophobic surface layer on the surface of the base material, protecting the base material from moisture erosion, and thereby improving the air stability and cycle stability of the lithium ion battery positive electrode material. At the same time, there is an appropriate uncoated area on the surface of the base material, which provides a channel for the diffusion of lithium ions, reduces the influence of inert coating fluorine-containing silane on the electrical performance of the lithium ion battery positive electrode material, and thereby improves the charge-discharge performance and energy density of the lithium ion battery positive electrode material. Therefore, the lithium ion battery in examples 1-6 can maintain good hydrophobicity and storage performance, and also improve the capacity performance and cycle performance of the lithium ion battery positive electrode material.

[0083] As shown in Figure 2 From the FE-SEM image of the lithium ion battery positive electrode material in example 1, it can be seen that there are many discrete point-like and island-like coatings on the surface of the lithium ion battery positive electrode material grain, and the distance between adjacent coatings is measured by Image J software, and the distance L is in the range of 8nm~400nm, satisfying 5nm≤L≤1000nm. Combined with the results of tables 1 to 3, it can be seen that the lithium ion battery positive electrode material in examples 1-6 has good hydrophobicity and storage performance, and also has good capacity performance and cycle performance. Figure 3 ​The XRD characteristic peaks of the lithium ion battery cathode material in Example 1 matched the standard PDF card (standard diffraction card) of the nickel-cobalt-manganese ternary material, and no impurity peaks appeared, indicating that the fluorine-containing silane coating did not affect the bulk structure of the base material. As can be seen from Tables 1-3, the initial residual alkali content of the lithium ion battery cathode material in Example 1 was 0.098wt%, the residual alkali content after 8 days of exposure was 0.109wt%, the initial moisture content was 125ppm, the moisture content after 8 days of exposure was 153ppm, the first circle discharge capacity was 226.10mAh / g, the first circle coulombic efficiency was 92.50%, after 50 cycles, the capacity retention rate was as high as 87.54%, the discharge capacity after 8 days of exposure was still as high as 225.96mAh / g, and the capacity retention rate after 50 cycles after 8 days of exposure was 87.25%, which showed that the lithium ion battery cathode material prepared in Example 1 had excellent hydrophobic performance and electrochemical performance.

[0084] As shown in FIG. 1, the FE-SEM image of the lithium ion battery cathode material in Example 1 showed that the surface of the material was covered with discrete point-like and island-like coatings. Figure 4 As shown in FIG. 2, the FE-SEM image of the lithium ion battery cathode material in Example 2 showed that the surface of the material was covered with discrete point-like and island-like coatings.

[0085] As shown in FIG. 3, the FE-SEM image of the lithium ion battery cathode material in Comparative Example 1 showed that the surface of the material was smooth, and no point-like and / or island-like coatings appeared. Figure 5 As shown in FIG. 4, the FE-SEM image of the lithium ion battery cathode material in Comparative Example 2 showed that the surface of the material was covered with discrete point-like and island-like coatings. Figure 6 As shown in FIG. 5, the FE-SEM image of the lithium ion battery cathode material in Comparative Example 3 showed that the surface of the material was covered with discrete point-like and island-like coatings. As shown in FIG. 6, the FE-SEM image of the lithium ion battery cathode material in Comparative Example 4 showed that the surface of the material was covered with discrete point-like and island-like coatings.

[0086] Compared with Example 1, the distance L between adjacent coatings in the FE-SEM observation of Comparative Example 2 ranges from 2 nm to 100 nm, which does not satisfy 5 nm≤L≤1000 nm, indicating that the spacing of the surface coatings of Comparative Example 2 is too small. The initial residual alkali content of the lithium ion battery cathode material in Comparative Example 2 is 0.037 wt%, the XRD characteristic peaks coincide with the nickel-cobalt-manganese ternary material PDF card, however, the first circle discharge capacity of Comparative Example 2 is only 217.73 mAh / g, the first circle coulombic efficiency is only 90.32%, and after 50 cycles, the capacity retention rate is only 64.52%. Combined with Figure 7 , analyzing the charge-discharge curves of Example 1 and Comparative Example 2, the initial polarization voltage of Example 1 is lower, while the initial polarization voltage of Comparative Example 2 is increased, which is due to the small spacing L of the coatings formed on the surface of the lithium ion battery cathode material of Comparative Example 2, which hinders the transmission channel of lithium ions, thereby causing the initial polarization voltage to increase and the discharge capacity to decrease. That is, although Comparative Example 2 can have hydrophobicity, its electrochemical performance is limited, while Example 1 can balance good hydrophobicity and electrochemical performance.

[0087] Combined with Table 2 and Table 3, the contact angles of the lithium ion battery cathode materials in Examples 1-6 are all higher than 150°, while the contact angles of Comparative Example 1 and Comparative Example 3 are 83° and 116° respectively, indicating that the dot-shaped and / or island-shaped coatings formed by fluorine-containing silane make the lithium ion battery cathode materials in Examples 1-6 have excellent hydrophobic properties. After being exposed to an air environment with a humidity of 60% for 8 days, the surface residual alkali and moisture increment of Examples 1-6 is minimal, indicating that the lithium ion battery cathode material has excellent air stability, at the same time, the discharge capacity and cycle retention rate of the battery of Examples 1-6 remain at the initial level after 8 days of exposure, indicating that the coatings effectively block the moisture in the air during the exposure process, without causing damage to the surface structure of the material. However, Comparative Example 1 does not have fluorine-containing silane coatings on the surface, and the spacing L of the coatings on the surface of Comparative Example 3 is too large, which reacts with the moisture in the air after exposure, resulting in a significant increase in residual alkali and an increase in side reactions with the electrolyte, thereby degrading the discharge capacity and cycle performance.

[0088] It can be understood that the above embodiments are only exemplary embodiments adopted to illustrate the principles of the present application, but the present application is not limited thereto. Various modifications and improvements can be made by those skilled in the art without departing from the spirit and essence of the present application, and these modifications and improvements are also considered to be within the protection scope of the present application.

Claims

1. A lithium-ion battery cathode material, characterized in that, include: The matrix material and a plurality of discrete coatings distributed on the surface of the matrix material, the coatings including fluorinated silanes, the mass ratio of the matrix material to all the coatings is 1:(0.001~0.25), and the shortest distance between any two adjacent coatings is L, where L satisfies: 5nm≤L≤1000nm.

2. The lithium-ion battery cathode material as described in claim 1, characterized in that, The mass ratio of the matrix material to all the coatings is 1:(0.02~0.12); the L satisfies 10nm≤L≤500nm.

3. The lithium-ion battery cathode material as described in claim 1, characterized in that, The coating is applied in a dotted and / or island-like manner on the surface of the matrix material.

4. The lithium-ion battery cathode material as described in claim 1, characterized in that, The maximum thickness of each of the aforementioned coatings is d, where d satisfies: 2nm ≤ d ≤ 100nm; and / or The surface roughness of the lithium-ion battery cathode material is Ra, which satisfies: 33nm≤Ra≤300nm.

5. The lithium-ion battery cathode material as described in claim 1, characterized in that, Each of the coatings has a size in the micrometer or nanometer range.

6. The lithium-ion battery cathode material as described in claim 1, characterized in that, The fluorinated silanes include at least one of 1H,1H,2H,2H-perfluorodecyltrichlorosilane, 1H,1H,2H,2H-perfluorodecyltriethoxysilane, heptadecafluorodecyltrimethoxysilane, dodecafluoroheptylpropyltrimethoxysilane, and dimethyl-γ-perfluorooctanoyloxypropylchlorosilane.

7. A method for preparing a lithium-ion battery cathode material, characterized in that, include: The precursor and lithium source of the lithium-ion battery cathode material are mixed and sintered once to obtain the matrix material. The matrix material and the coating material are mixed to obtain a mixture, wherein the mass ratio of the matrix material to the coating material is 1:(0.001~0.25), and the coating material includes a fluorosilane; and The mixture is sintered a second time to form multiple discrete coatings distributed on the surface of the matrix material, thereby obtaining the lithium-ion battery cathode material. The shortest distance between any two adjacent coatings is L, and L satisfies: 5nm≤L≤1000nm.

8. The preparation method according to claim 7, characterized in that, The secondary sintering includes a first stage sintering and a second stage sintering performed sequentially, wherein the pressure of the first stage sintering is 1 Pa to 15 Pa, and the pressure of the second stage sintering is -30 Pa to -5 Pa.

9. The preparation method according to claim 8, characterized in that, The sintering temperature of the first stage is 50℃~300℃, and the sintering time of the first stage is 0.5h~10h; the sintering temperature of the second stage is 200℃~500℃, and the sintering time of the second stage is 2h~10h.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode material, the positive electrode material being a lithium-ion battery positive electrode material as described in any one of claims 1 to 6 or a lithium-ion battery positive electrode material prepared by the preparation method as described in any one of claims 7 to 9.

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